The field of the invention is automated processing systems used for processing semiconductor wafers, hard disk media, substrates, and similar flat media.
Electronic products, for example, computers, televisions, telephones, etc., contain large numbers of electronic semiconductor devices. To produce these electronic products, hundreds or thousands of semiconductor devices are manufactured in a very small space, using lithography techniques on semiconductor substrates, such as on silicon wafers. A large number of individual processing steps may be required to manufacture the semiconductor devices. Various machines and methods have been developed to manufacture semiconductor devices. For example, U.S. Pat. No. 6,279,724, incorporated herein by reference, describes a system having processing chambers for processing and cleaning flat media, referred to herein as xe2x80x9cwafersxe2x80x9d.
In various processing steps, it is necessary to apply or spray different chemical solutions onto the wafers. The chemical solutions, which can contain several different liquid ingredients, must be prepared with precise amounts of the ingredients, to maintain uniform processing of the wafers. Typical wafer processing systems have several processing chambers, with at least one chemical solution process tank associated with each process chamber, for storing the chemical solution used in the process chamber. A chemical solution handling or delivery system associated with each process tank and process chamber, mixes, stores, heats, recirculates, and delivers the chemical solutions to the process chamber.
Wafer throughput is a critical performance parameter for semiconductor processing equipment. To achieve maximum wafer throughput, the chemical process chamber (CPC) must operate at 100% availability. In other words, the CPC must be able to operate when needed, without delays required for preparing the chemical solutions. In processing where several chemical solutions are used sequentially, each chemical solution must be available to the CPC in sequence at the required time, without delays, to operate at 100% availability. Each process step within the CPC takes a specific amount of time. In addition, each chemical solution has a specific bath life, (e.g., 4 hours), and beyond which the chemical solution looses its ability to further adequately process wafers, and it must therefore then be discarded. For maximum throughput, the chemical process tank must thereafter be replenished with fresh chemical solution, within a time less than the sum of the process times of all of the other process steps.
For each process step, the chemical solution accuracy, and temperature stability of the chemical solution, greatly affects the wafer processing rate and wafer processing uniformity. Preferably, chemical solution accuracy is maintained to within 1%, and chemical solution temperature is maintained to a tolerance of plus or minus 1xc2x0 C. of the temperature set point. However, these design goals have been difficult or impossible to meet.
The chemical solutions used in semiconductor processing can be costly. In addition, handling and disposal of some of these types of chemical solutions can also be costly and time consuming. It is therefore advantageous to use the least amount of chemical solution as possible, while maintaining a desired wafer processing rate, consistency, and quality.
In the past, wafer processing systems, such as described in U.S. Pat. No. 5,664,337, incorporated herein by reference, have used relatively large (e.g., 12 gallon) process tanks. These large tanks have required in excess of 16 minutes to heat the chemical solutions from room temperature to a temperature set point of 70xc2x0 C. The chemical solution handling or delivery system in these known wafer processors also measure out the chemical solutions in a mixture using a metering pump. As metering pumps have a known error per stroke that accumulates as a volume of chemical solution is delivered, chemical solution accuracy has not been tightly controlled. Use of the metering pump also results in a more complex design, which can impair reliability and increase cost of manufacture.
Accordingly, it is an object of the invention to provide an improved system for handling and delivering chemical solutions in a semiconductor processing system. Other features and advantages will appear hereinafter.
To these ends, in a first aspect of the invention, a system for delivering a chemical solution to a processing chamber includes a metering vessel and a process tank. Level detectors in the metering vessel and process tank detect liquid levels. A dispense valve on the metering vessel allows the liquid chemical solution component to flow from the metering vessel into the process tank, preferably via gravity. Metering errors accumulating from use of a metering pump are eliminated.
In a second and separate aspect of the invention, the metering vessel has a two stage fill valve assembly, including a first or fast fill valve, and a second or slow fill valve. The first fill valve and the second fill valve both open to rapidly fill the metering vessel to near full. The second valve then closes to restrict flow through a smaller orifice, so the metering vessel continues to fill but at a slower rate, until the metering vessel is full. The metering vessel is quickly filled with a precise volume of liquid.
In a third and separate aspect of the invention, the metering vessel is filled from the bottom, to provide more accurate metering.
In a fourth and separate aspect of the invention, the metering vessel, valves, and other connections and components are supported on a lid of the tank. The process tank can then be removed from the system without disconnecting the various plumbing lines.